Current divider circuit for high current tap changing under load mechanism



R. L. DAVIS 2,830,254 CURRENT DIVIDER CIRCUIT FOR HIGH CURRENT TAP CHANGING UNDER LOAD MECHANISM Filed Dec. 10, 1954 April 8,1958

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INVENTOR.

RAYMOND L..DAVIS BY r 2,830,254 1C6 Patented AP 1958 CURRENT DIVIDER CIRCUIT FOR HIGH CUR- RENT TAP CHANGING UNDER LOAD MECH- ANISM Raymond L. Davis, Richmond Heights, Mo., assignor t Moloney Electric Company, St. Louis, Mo., a corporation of Delaware Application December 10, 1954, Serial No. 474,526

7 Claims. (Cl. 323-435) This invention relates generally to voltage regulating systems and more specifically to such voltage regulating systems which include regulating transformers having as sociated therewith tap changing apparatus designed for operation while the regulating transformer is under load, and which includes a load transfer switch with at least two paralleled tap changing under load contacts whose contact resistances may differ thus causing an unequal current division between the two contacts, with the resultant objection that the contact having the least contact resistance may be severely overloaded, depending on the magnitude of the difference in resistance, the predominant object being to provide a load current interrupting means which is so constructed and arranged that the current is divided equally between the two paralleled tap changing under load contacts to avoid the undesirable unequal current division referred to above.

Another important object of the invention is to provide a system of the type described above which has the advantage that it presents no insulation problems affecting the physical size of the device which might tend to make it big and bulky, and also the mounting problem is eliminated because certain leads of the system could be designed to support ring-type current transformers forming part of the circuit.

Fig. 1 is a diagrammatical and schematic view of the circuit of the present invention.

Fig. 2 is a view of the circuit shown in Fig. 1, but showing the circuit schematically only, through the use of certain standard electrical symbols.

Fig. 3 is a diagrammatical and schematic view showing a modified form of the invention.

The load current interrupting means A shown in Fig. 1 includes load transfer switch having a pair of stationary contacts 1 with each of which is associated a moving contact 2 that concurrently contacts the surfaces of said stationary contacts and with a collector ring 3. The electrical circuit A includes a pair of current transformers 4 and 5, preferably of the ring-type, and these ring-type current transformers are supported by the leads 4 and 5' which are connected to the collector rings 3 and spliced at 6 to a conductor 7 which leads from bushing 8 projected from insulating panel 9. The stationary contacts have extended therefrom conductors 10 and 11, which are in turn connected to a conductor 12. By referring to Figs. 1 and 2 it will be noted that the secondaries 13 of the current transformers 4 and 5 are cross connected and this arrangement constitutes the predominant feature of the invention inasmuch as the primary currents are forced to be equal. This is brought about by the fact that the leg of the circuit whose contact resistance is smaller will tend to have the larger current, but with this larger current will come a high impedance in its current transformer primary because it is trying to drive the other current transformer primary, in this case the current transformer primary is one turn or the lead through the ring-type current transformer. This induced impedance sets up a voltage, and it will be assumed in this case this voltage is V and impedes the flow of current I until it equals the flow of current 1 Then V V but V +V =V +V with the result that the circuit is satisfied, and 1 :1

Fig. 3 illustrates a modified form of the circuit in which the location of the current transformers would oifer a great advantage in mechanical design. The advantage of the arrangement illustrated in Fig. 3 over that shown in Figs. 1 and 2 is that only one common collector ring 14, or other device, for both moving contacts 15 and both stationary contacts 16 is needed, the current transformers being designated by the reference characters 17 and 18, and secondaries 19 of said transformers being cross connected as indicated at 28. In Fig. 3 insulated contact supports 21 are provided.

I claim:

1. in a tap changing under load regulating transformer, load current interrupting means comprising a load transfer switch, said switch having at least two stationary contact surfaces and two movable contacts, each of the movable contacts adapted to bear respectively and concurrently against each of the stationary contact surfaces, said stationary contact surfaces being electrically connected to a single voltage point, the electrical connections thereby formed between each of said movable contacts and said stationary contact surfaces having respective independent contact resistance values, each of said movable contacts being adapted to carry a part of said load current, a pair of current transformers each having a primary responsive respectively to the current carried by each contact, said current transformers having secondaries which are cross-connected, whereby the current carried by each of said contacts is maintained approximately equal independently of variations in said respective contact resistances.

2. in a tap changing under load regulating transformer, 21 load interrupting means as set forth in claim 1 in which said current transformers are of the ring type. v

3. In a tap-changing under load regulating transformer, load current interrupting means comprising a load transfer switch, said switch having at least two stationary contacts and two movable contacts, each movable contact adapted to bear respectively and concurrently against each of the stationary contacts, said stationary contact surfaces being electrically connected to a single voltage point, the electrical connections thereby formed between each of said movable contacts and said stationary contact having respective independent contact resistance values, an electrical conductor connected to each of said movable contacts adapted to carry part of the load current, a pair of current transformers each having a primary carrying the current of one of. the electrical conductors, said current transformers having secondaries which are cross connected, whereby the current carried by each of said conductors is maintained approximately equal independently of variations in said respective contact resistances.

4. In a tap-changing under load regulating transformer,

a load interrupting means as set forth in claim 3 in which said current transformers are of the ring type.

5. In a tap-changing under load regulating transformer, a load interrupting means as set forth in claim 4 in which said currenttrans'formersare supported by said conducsaid current transformers are of the ring type and are torsandsaidconductors comprise the respective current supported by said conductors, said conductors compristransformer primaries. ing the respective current transformer primaries.

6. In a tap-changing under load regulating transformer, a load interrupting means as set forth in claim 3 which 5 References Clted 111 i116 file Of this Patent further includes electrical collecting means to which each UNITED STATES PATENTS at said electrical conductorsare connected by an electrical 1,162,405 Schweitzer 30 1915 rus 7. In atap-c'hanging under load regulating transformer, FOREIGN PATENTS a load interrupting means asset-forth inciaimfiin which 10 368,475 Great Britain Mar. 10, 1932 

